# CVE-2026-23518: Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment > Attackers can forge JWT tokens to enroll unauthorized devices under arbitrary user identities due to missing signature verification in Fleet's Windows MDM enrollment. - **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 21 Jan 2026 - **Updated:** 22 Jan 2026 - **Also known as:** GHSA-63m5-974w-448v, GO-2026-4335 ## What is CVE-2026-23518? CVE-2026-23518 is a critical authentication bypass vulnerability in fleetdm fleet, published on 21 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description Fleet is open source device management software. In versions prior to 4.78.3, 4.77.1, 4.76.2, 4.75.2, and 4.53.3, a vulnerability in Fleet's Windows MDM enrollment flow could allow an attacker to submit forged authentication tokens that are not properly validated. Because JWT signatures were not verified, Fleet could accept attacker-controlled identity claims, enabling enrollment of unauthorized devices under arbitrary Azure AD user identities. Versions 4.78.3, 4.77.1, 4.76.2, 4.75.2, and 4.53.3 fix the issue. If an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM. Weakness: CWE-347 (Improper Verification of Cryptographic Signature) ## Which versions are affected by CVE-2026-23518? 11 open source packages ship an affected version, including github.com/fleetdm/fleet and github.com/fleetdm/fleet/v4. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `github.com/fleetdm/fleet` | Go | All versions | 4.43.5-0.20260112202845-e225ef57912c | | `github.com/fleetdm/fleet` | Go | All versions | 4.43.5-0.20260112202845-e225ef57912c | | `github.com/fleetdm/fleet` | Go | From 4.75.0 | 4.75.2 | | `github.com/fleetdm/fleet` | Go | From 4.75.0 | 4.75.2 | | `github.com/fleetdm/fleet` | Go | From 4.76.0 | 4.76.2 | | `github.com/fleetdm/fleet` | Go | From 4.76.0 | 4.76.2 | | `github.com/fleetdm/fleet` | Go | From 4.77.0 | 4.77.1 | | `github.com/fleetdm/fleet` | Go | From 4.77.0 | 4.77.1 | | `github.com/fleetdm/fleet` | Go | From 4.78.0 | 4.78.3 | | `github.com/fleetdm/fleet` | Go | From 4.78.0 | 4.78.3 | | `github.com/fleetdm/fleet/v4` | Go | From 4.75.0 | 4.75.2, 4.76.2, 4.77.1, 4.78.3 | Products: Fleetdm Fleet. ## How do I fix CVE-2026-23518? Upgrade github.com/fleetdm/fleet to a fixed version for your release line: 4.43.5-0.20260112202845-e225ef57912c, 4.75.2, 4.76.2 or 4.77.1. ## Is CVE-2026-23518 being exploited? There is no known exploitation of CVE-2026-23518 in the wild and no public exploit code. ## Other vulnerabilities in fleetdm fleet - [CVE-2020-26276](https://insights.sbomify.com/CVE-2020-26276/): SAML authentication vulnerability in Fleet (critical 10.0) - [CVE-2026-103264](https://insights.sbomify.com/CVE-2026-103264/): Fleet before 4.87.0 Authentication Bypass via Device Identifiers (critical 9.3) - [CVE-2026-26062](https://insights.sbomify.com/CVE-2026-26062/): Fleet server may terminate unexpectedly when handling certain gRPC requests (high 8.7) - [CVE-2026-26061](https://insights.sbomify.com/CVE-2026-26061/): Fleet's unbounded request body read allows remote Denial of Service (high 8.7) - [CVE-2026-23998](https://insights.sbomify.com/CVE-2026-23998/): Fleet has a Windows MDM management endpoint authentication bypass (high 8.2) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-23518 and fix it if it is affected. What it is: CVE-2026-23518 is a critical authentication bypass vulnerability in fleetdm fleet, published on 21 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-23518 in the wild and no public exploit code. Affected packages and fixed versions: - github.com/fleetdm/fleet (Go): affected all versions; fixed in 4.43.5-0.20260112202845-e225ef57912c - github.com/fleetdm/fleet (Go): affected all versions; fixed in 4.43.5-0.20260112202845-e225ef57912c - github.com/fleetdm/fleet (Go): affected from 4.75.0; fixed in 4.75.2 - github.com/fleetdm/fleet (Go): affected from 4.75.0; fixed in 4.75.2 - github.com/fleetdm/fleet (Go): affected from 4.76.0; fixed in 4.76.2 - github.com/fleetdm/fleet (Go): affected from 4.76.0; fixed in 4.76.2 - github.com/fleetdm/fleet (Go): affected from 4.77.0; fixed in 4.77.1 - github.com/fleetdm/fleet (Go): affected from 4.77.0; fixed in 4.77.1 - github.com/fleetdm/fleet (Go): affected from 4.78.0; fixed in 4.78.3 - github.com/fleetdm/fleet (Go): affected from 4.78.0; fixed in 4.78.3 - github.com/fleetdm/fleet/v4 (Go): affected from 4.75.0; fixed in 4.75.2, 4.76.2, 4.77.1, 4.78.3 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-23518/ (Markdown: https://insights.sbomify.com/CVE-2026-23518/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23518 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23518 - OSV: https://osv.dev/vulnerability/CVE-2026-23518 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-23518/ Summaries are generated and may contain mistakes; the official description above is the record.